Why do I still hear faint white noise from my amp when I have Standby on?
Historically, not all tube amplifiers had Standby switches, and some modern amps are forgoing it thanks to advancements in technology (and consumer education).
On some PRS amp designs that do feature Standby switches such as the PRS MT 15 and PRS Sonzera 20, the circuit is designed to leave the power amp section on while muting the pre-amp section of the amp as a convenience, thus eliminating possible noises while Standby is engaged during any short breaks. Standby switches were never meant to be used while taking a break on stage. If you take a long break, simply turn the amp off.
Amps, like well-tuned gas-powered cars, will have an idling sound before you hit the gas and rev it up. In short, if you hear a faint white noise from your amp in Standby mode, it's not a problem, but rather an indication that your amp is ready to rock.
Why doesn’t my amp have a standby switch?
The Standby switch has been a controversial component in amplifier design, with some modern amps forgoing it thanks to advancements in technology (and consumer education).
Historically, not all tube amplifiers had Standby switches. The PRS HDRX 100 and 50, for example, do not feature Standby switches. To mute the amp between sets, simply pull the guitar cable plug out one notch at the input jack.
Leo Fender was likely the first to include a Standby switch on a guitar amp to protect power supply capacitors from high voltages caused by cold tubes. However, changes in rectifier and capacitor technology have negated the absolute need for these switches.
A common misconception around Standby switches is that they can extend tube life. However, this only applies to transmitting tubes, not receiving tubes as used in guitar amps. Receiving tubes do not need to have the B+ or plate voltage removed while the filaments warm up.
And finally, since traditional standby switches handle very high DC voltages, they can sometimes develop internal arcs when opening or closing that come through the speaker as a loud pop. While this is more of an irritation and anything, it often requires replacing the switch or adding components to the switch to remedy.